This invention relates to systems and methods for delivering pressurized liquefied natural gas to an import terminal that contains storage tanks and vaporization facilities suitable for conventional liquefied natural gas at atmospheric pressure. The pressurized liquefied natural gas cargo, or any fraction thereof, is converted into conventional liquefied natural gas and sent to storage tanks suitable for conventional liquefied natural gas. Any of the cargo not converted to conventional liquefied natural gas can be compressed and warmed to pipeline specifications. This gas can then pass into a sendout pipeline.
Various terms are defined in the following specification. For convenience, a Glossary of terms is provided herein, immediately preceding the claims.
Large volumes of natural gas (i.e. primarily methane) are produced in remote areas of the world. This gas has significant value if it can be economically transported to market. Where the production area is in reasonable proximity to a market and the terrain between the two locations permits, the gas is typically transported through submerged and/or land-based pipelines. However, when gas is produced in locations where laying a pipeline is infeasible or economically prohibitive, other techniques must be used for getting this gas to market.
A commonly used technique for non-pipeline transport of gas involves liquefying the gas at or near the production site and then transporting the liquefied natural gas to market in specially-designed storage tanks aboard transport vessels. The natural gas is cooled and condensed to a liquid state to produce liquefied natural gas at substantially atmospheric pressure and at temperatures of about xe2x88x92162xc2x0 C. (xe2x88x92260xc2x0 F.) (xe2x80x9cLNGxe2x80x9d), thereby significantly increasing the amount of gas which can be stored in a particular storage tank. Once an LNG transport vessel reaches its destination, the LNG is typically off-loaded into other storage tanks from which the LNG can then be revaporized as needed and transported as a gas to end users through pipelines or the like.
U.S. Pat. No. 6,085,528 (the xe2x80x9cPLNG Patentxe2x80x9d), having corresponding International Publication Number WO 98/59085, and entitled xe2x80x9cImproved System for Processing, Storing, and Transporting Liquefied Natural Gasxe2x80x9d, describes containers and transportation vessels for storage and marine transportation of pressurized liquefied natural gas (PLNG) at a pressure in the broad range of about 1035 kPa (150 psia) to about 7590 kPa (1100 psia) and at a temperature in the broad range of about xe2x88x92123xc2x0 C. (xe2x88x92190xc2x0 F.) to about xe2x88x9262xc2x0 C. (xe2x88x9280xc2x0 F.). Containers described in the PLNG Patent are constructed from ultra-high strength, low alloy steels containing less than 9 wt % nickel and having tensile strengths greater than 830 MPa (120 ksi) and adequate toughness for containing PLNG. U.S. patent application Ser. No. 09/495,831 (the xe2x80x9cPLNG Patent Applicationxe2x80x9d), having corresponding International Publication Number WO 00/57102, and entitled xe2x80x9cImproved System and Methods for Producing and Storing Liquefied Natural Gasxe2x80x9d, also describes containers for storage and transport of PLNG. Containers described in the PLNG Patent Application comprise a load-bearing vessel made from a composite material and a substantially impermeable, non-load-bearing liner in contact with the vessel. Any container suitable for storing PLNG shall be referred to hereinafter as a PLNG Container. Any container suitable for storing LNG that is not also suitable for storing PLNG shall be referred to hereinafter as an LNG Container. The PLNG Patent and the PLNG Patent Application are hereby incorporated herein by reference.
PLNG may be unloaded at an import terminal into pressurized PLNG Containers, e.g., by using some of the displaced vapors to maintain a minimum required pressure in the PLNG Containers on the transport ship. However, it may be desirable to deliver PLNG to a conventional LNG import terminal that is equipped with conventional LNG Containers but is not equipped with PLNG Containers
In spite of the aforementioned advances in technology, to our knowledge, systems and methods for delivering PLNG to an import terminal equipped with LNG Containers and vaporization facilities suitable for LNG, do not currently exist. It would be advantageous to have such systems and methods.
Therefore, an object of this invention is to provide such systems and methods. Other objects of this invention will be made apparent by the following description of the invention.
Consistent with the above-stated objects of the present invention, systems and methods for delivering PLNG to an import terminal equipped with LNG Containers and vaporization facilities suitable for LNG are provided. A system according to the present invention comprises: (a) pressurized liquefied natural gas at a pressure of about 1035 kPa (150 psia) to about 7590 kPa (1100 psia) and at a temperature of about xe2x88x92123xc2x0 C. (xe2x88x92190xc2x0 F.) to about xe2x88x9262xc2x0 C. (xe2x88x9280xc2x0 F.) stored in one or more PLNG Containers having adequate strength and toughness to contain said pressurized liquefied natural gas at said pressure and temperature conditions; (b) one or more LNG Containers suitable for storing liquefied natural gas at substantially atmospheric pressure and at a temperature of about xe2x88x92162xc2x0 C. (xe2x88x92260xc2x0 F.); (c) means for removing and reducing the pressure of at least a portion of said pressurized liquefied natural gas from said one or more PLNG Containers, which removed pressurized liquefied natural gas comprises a substantially gaseous portion and a substantially liquid portion; (d) separation equipment suitable for separating said substantially gaseous portion and said substantially-liquid portion; (e) pressurization equipment suitable for pressurizing said substantially gaseous portion to a desired pressure; (f) gas delivery equipment suitable for delivering said pressurized substantially gaseous portion to a gaseous portion destination; (g) depressurization equipment suitable for reducing the pressure of said substantially liquid portion to substantially atmospheric pressure in one or more steps; and (h) liquid delivery equipment suitable for delivering said substantially atmospheric pressure liquid portion to said one or more LNG Containers. In one embodiment, the means for reducing the pressure of at least a portion of the pressurized liquefied natural gas consists essentially of expansion. A method according to the present invention comprises the steps: (a) storing pressurized liquefied natural gas at a pressure of about 1035 kPa (150 psia) to about 7590 kPa (1100 psia) and at a temperature of about xe2x88x92123xc2x0 C. (xe2x88x92190xc2x0 F.) to about xe2x88x9262xc2x0 C. (xe2x88x9280xc2x0 F.) in one or more PLNG Containers having adequate strength and toughness to contain said pressurized liquefied natural gas at said pressure and temperature conditions; (b) removing and reducing the pressure of at least a portion of said pressurized liquefied natural gas from said one or more PLNG Containers, which removed pressurized liquefied natural gas comprises a substantially gaseous portion and a substantially liquid portion; (c) separating said substantially gaseous portion and said substantially liquid portion; (d) pressurizing said substantially gaseous portion to a desired pressure; (e) delivering said pressurized substantially gaseous portion to a gaseous portion destination; (f) reducing the pressure of said substantially liquid portion to substantially atmospheric pressure in one or more steps; and (g) delivering said substantially atmospheric pressure liquid portion to one or more LNG Containers suitable for storing liquefied natural gas at substantially atmospheric pressure and at a temperature of about xe2x88x92162xc2x0 C. (xe2x88x92260xc2x0 F.). In the process of removing PLNG from said PLNG Containers, displacement vapor may be used to maintain pressure and prevent auto-refrigeration of the remaining cargo. In one embodiment, reducing the pressure of at least a portion of the pressurized liquefied natural gas consists essentially of expanding the pressurized liquefied natural gas.
All of, or a portion of, the PLNG is let down through one or more liquid expanders and/or control valve, such as Joule-Thompson valves, in series to the LNG Containers. Resulting flash vapors are collected from flash vessels downstream of the expanders and control valves and fed to a compression system designed to recompress the vapors to pipeline delivery pressure. Displacement vapors for unloading the PLNG Containers on the transport ship can be withdrawn, as needed, from the vapors being recompressed to the sales gas pipeline.
In one embodiment, the predominantly isenthalpic and/or isentropic expansion and partial vaporization of the pressurized cryogenic liquid streams can provide substantially all the refrigeration needed for cooling the remaining (unvaporized) liquid. The end result is a conventional LNG product that has been cooled to its bubble point temperature at essentially atmospheric pressure. This liquid can then be stored in existing conventional LNG import terminal facilities, including LNG Containers, and eventually revaporized for use. If only a portion of the PLNG is let down in pressure, the remaining PLNG can be unloaded and vaporized by any available method, for example without limiting this invention, by the methods described in U.S. Pat. No. 6,112,528.